Heat exchange apparatus, e. g. for use in gas turbine engines



Jan.- 7, 1964 N. H. KENT ,7

HEAT EXCHANGE APPARATUS, E.G. FOR UsE IN GAS TURBINE ENGINES Filed March3, 1961 -4 Shets-Shet 1 Attorneys Jan. 7, 1964 N. H. KENT 3,

HEAT EXCHANGE APPARATUS; EL'G. FOR 'USE IN GAS TURBINE ENGINES FiledMarch 5, 1961 4 Sheets-Shet 2 Inventor P MM KM f wwrwm Attorneys Jan. 7,1964 N. H. KENT 3,116,789

HEAT EXCHANGE APPARATUS, E.G. FOR USE IN GAS TURBINE ENGINES Filed March3, 1961 4 Sheets-Sheet 5 IIIL- Attorneys Jan. 7, 1964 KENT 3,116,789

HEAT EXCH ANGE APPARATUS, E.G. FOR USE IN GAS TURBINE ENGINES FiledMarch 3, 1961 4 Sheets-Sheet 4 v Q /7 26 Q 9 L w 76 /6 "\3:II-T 74 I 5869 v I Inventor W az vawzm Attorneys United States Patent 3,136,789 HEATEXCHANGE APPARATUSS, EG. FGR USE liN GAS TURBINE ENGINES Nelson HectorKent, Derby, England, assignor to Rolls- Royce Limited, Derby, England,a company of Great Britain Filed Mar. 3, 19:51, Ser. No. 93,269 Claimsprierity, application Great Britain Mar. 14, 19W 9 Clm'ms. (Cl. 165-147)This invention concerns heat exchange apparatus and, although it is notso restricted, it is more particularly concerned with anti-icingapparatus for a gas turbine engine.

A gas turbine engine is commonly provided at its upstream end with abullet-shaped internal wall member which is mounted within the enginecasing and defines therewith an annular air intake. The bullet-shapedinternal wall member carries one of the engine bearings and is supportedfrom the engine casing by substantially radial struts which, inoperation, are liable to act as collecting surfaces for ice. It will beappreciated that if these struts are heated so as to de-ice them, it isimportant that they should be heated to an equal extent if buckling ofthe struts and consequent misalignment of the said bearing is to beavoided.

In co-pending application Serial No. 41,347, dated July 7, 1960, nowPatent No. 3,057,154, filed by William Sherlaw et al., there isdisclosed an anti-icing apparatus in which these struts are hollow andidentical, and communicate with successive parts of a common annularmanifold of uniform cross-sectional area carried by the engine casing,the manifold being connected by a supply pipe to the outlet of a highpressure compressor of the engine so as to receive therefrom air Whichhas been heated by being compressed. By this means all the struts aresupplied with air at substantially the same temperature. We have nowfound, however, that the total pressure head i.e. the sum of the staticpressure head and the velocity pressure head in the manifold downstreamof each strut is, by reason of the air supplied to the strut, lower thanthe total pressure head upstream thereof. Hence the total pressure headsin the strut inlets furthest removed from the said supply pipe aresubstantially lower than the total pressure heads in the strut inletsnearest to the said supply pipe. These total pressure head differencesgive rise to unequal heating of the struts.

According to the present invention there is provided heat exchangeapparatus comprising two spaced apart members which are connectedtogether by a plurality of struts, a plurality of fluid ducts each ofwhich is in heat exchange relationship with a respective strut, saidfluid ducts being connected by way of fluid supply manifold means to acommon means which supplies thereto a pressure fluid at a temperaturehigher than that of said struts, the fluid path along which the fluidflows from said common means to exhaust by way of said supply manifoldmeans and said fluid ducts being such, that the total pre sure heads atthe inlets to said fluid ducts are substantially equal, and that thefluid heats said struts so that they expand by substantially equalamounts.

Said supply manifold means may comprise a separate manifold for eachfluid duct. Alternatively said supply manifold means may include amanifold, said ducts communicating with said manifold at points whichare spaced along the length thereof, the cross sectional area of saidmanifold decreasing in the downstream direction of fluid flowtherethrough so that the total pressure head therein remainssubstantially constant.

Alternatively, said supply manifold means may include several manifoldseach feeding a respective proportion of the ducts in succession. In thiscase, a substantially constant total pressure head can be maintained ineach manialiases ice' fold if the cross sectional area of each manifoldis such that the velocity pressure head along its length isinsignificant. The necessary size of the manifolds would however makethis possibility impractical for certain applications. Alternatively,the manifolds can be supplied with a static pressure head with which thevelocity pressure head in the manifolds is insignificant in comparison,in which case the size of the manifolds can be reduced. Preferably anarrangement between these two extremes is adapted where the staticpressure head within the manifolds is comparatively low e.g. of theorder of the static pressure head at the outlet of a low pressurecompressor of a gas turbine engine, each manifold having a sufficientlylarge cross sectional area so that the velocity pressure head therein isinsignificant compared with the static pressure head therein.

The fluid from the fluid ducts can flow directly to the atmosphere, butpreferably, exhaust manifold means is provided which communicates withsaid fluid ducts and guides the fluid from the ducts to exhaust. Theexhaust manifold means may be constructed in any of the different Waysdescribed for said supply manifold means.

Preferably said supply manifold means and said exhaust manifold meansare mounted one within the other, each manifold means communcating withsaid fluid ducts in succession so that fluid can flow from the supplymanifold means via the fluid ducts to the space between the supply andexhaust manifold means, the total internal cross-sectional area of theinner manifold means diminishing in the downstream direction of fluidflow therethrough, and the cross-sectional area between the supply andexhaust manifold means increasing in the downstream direction of fluidflow therethrough.

Preferably the internal cross-sectional area defined by the internalwalls of the outer manifold means is substantially constant.

One convenient arrangement is to dispose the supply manifold meanswithin the exhaust manifold means.

The supply manifold means (and the exhaust manifold means where one isprovided) may be arcuate and the ducts may be arranged substantiallyradially thereof.

Preferably each duct is open-ended and is mounted within the respectivestrut with a space therebetween, the fluid flowing through the duct andthen flowing in the opposite direction through the space between theduct and the strut. It will be appreciated that the fluid can first flowthrough said space and then through the duct.

Preferably the spaces between the struts and the ducts adjacent the openends of the ducts intercommunicate with one another so as to permit thefluid pressures adjacent said open ends to equalise.

The invention also comprises a gas turbine engine provided with suchheat-exchange apparatus.

Thus in its preferred form the invention provides a gas turbine enginecomprising an engine casing, internal wall means mounted within saidcasing by means of a plurality of substantially radial struts, saidinternal wall means defining an annular air intake with said casing,arcuate fluid supply manifold means, a fluid inlet condult communicatingwith said fluid supply manifold means and with a supply of heated fluidunder pressure and at a temperature higher than that of said struts, aplurality of ducts each of which is arranged in heat exchangerelationship with a respective strut, said ducts communicating with saidfluid supply manifold means at angularly spaced apart points which arearranged to be successively supplied with fluid from the fluid inletconduit, the fluid paths along which the fluid flows from said fluidinlet conduit to exhaust by way of said fluid supply manifold means andsaid fluid ducts being such, that the total pressure heads at the inletsto said fluid ducts are substantially at equal, and that the fluid heatssaid struts so that they expand by substantially equal amounts.

The invention is illustrated, merely by way of example in theaccompanying drawings in which:

FIGURE 1 is a diagrammatic view, partly in section, of a gas turbineengine embodying the present invention,

FIGURE 2 is a section taken on the line 2-2 of FIG- URE 1,

FIGURE 3 is a section taken on the line 33 of FIG- URE 2.

FIGURE 4 is a developed plan view of part of the structure shown inFIGURES 1 to 3,

FIGURE 5 is a view corresponding to FIGURE 4 but illustrating amodification,

FIGURE 6 is a sectional view of part of the structure shown in FIGURE 5,

FIGURE 7 is a cross-sectional side elevation showing details of an inletpipe leading to a chamber with which fluid supply manifold meanscommunicates, the arrangement forming part of a modified form of theinvention,

FIGURE 8 is a plan view of FIGURE 7, with the inlet pipe and manifoldremoved,

FIGURE 9 is a cross-sectional view showing how a strut spaced from thechamber is connected to the fluid supply manifold means,

FIGURE 10 is a cross-sectional view of the hub shown in FIGURE 9 takenon the line XX,

FIGURE 11 is a cross-sectional view on the line XIXI of FIGURE 9, and

FIGURE 12 is a cross-sectional view taken on the line XII-XII of FIGURE9.

Referring to the drawings, a gas turbine jet propulsion engine for anaircraft comprises an engine casing 10 within which are arranged in flowseries an annular air intake 11, a compressor 12, combustion equipment13, and turbine 14, the exhaust gases from the turbine 14 beingdischarged to atmosphere through a jet pipe 15.

The annular air intake 11 is defined between the engine casing 10 and abullet-shaped air intake baffle or nose cone 16. The latter is mountedwithin the engine casing 10 by means of twelve hollow, aerofoil-shapedstruts 17 which extend between the nose cone 16 and the engine casing 14The nose cone 16 has mounted within it a bearing (not shown) for a shaft18 on which the compressor 12 and turbine 14 are mounted. Each of thestruts 17 extends tangentially of the nose cone 16 so as to diminish thebuckling effect of differential expansion and contraction of the struts17.

Mounted about and adjacent to the forward end of the engine casing 10 isan annular air exhaust manifold 19. The manifold 19, which is providedwith an exhaust port 20, communicates with the interiors of the hollowstruts 17.

Within the manifold 19 is a chamber 21. The chamber 21 does notcommunicate with the manifold 19 but is connected by a fluid inletconduit in the form of a pipe 22 to the outlet of the compressor 12 soas to receive therefrom a supply of air which has been heated by beingcompressed.

The chamber 21 (see FIGURE 4) communicates with a pair of aligned pipes23 and with a pair of aligned pipes 24 which extend beyond the pipes 23,the remote ends of the pipes 23, 24 being closed. The pipes 23, 24extend alongside each other and collectively constitute air inletmanifold means. As will be seen from FIGURE 4, the total cross-sectionalarea of the air inlet manifold means constituted by pipes 23, 24diminishes with increased distance from the pipe 22 where the pipes 23terminate. The pipes 23, 24 are spaced from the engine casing 10 byheat-insulating blocks 25.

Each of the twelve hollow struts 17 has a pipe 26 mounted within it.Each pipe 26 is spaced from the front and rear ends of its strut -17 asindicated at 27 and each pipe 26 has an open end 28 which is spaced fromthe nose cone 16. Thus air heated in the compressor 12 it. may flow viathe pipe 22, chamber 21, pipes 23, 24, and pipes 26 to the interiors ofthe struts 17. As indicated by the arrow 29, the air then flows throughthe spaces 27, so as to heat the struts 17, and thence via the manifold19 to the exhaust port 20.

Seven of the twelve pipes 26 communicate with the pipes 23, while theremaining five pipes 26 communicate with the pipes 24. It will be notedthat the pipes 26 nearest to the chamber 21 communicate with the pipes23 whilst those furthest from the chamber 21 communicate with the pipes24.

Assuming that the internal cross-sectional area of pipes 23, 24 isuniform, and that air in the pipes 23, 24 accelerates into the inlet ofeach pipe 26, the total pressure head of the air in each of the pipes23, 24 downstream of its junction with a pipe 26, will, by reason of theair supplied to the pipe 26, be lower than the total pressure headupstream thereof.

In other words, there is a total pressure head drop at each junctionwith a pipe 26 and if all twelve pipes 26 were supplied from the twopipes 23, or the two pipes 24, the total pressure head in the pipes 26furthest removed from the chamber 21 would be substantially less thanthe total pressure head in the pipes 26 nearest to the chamber 21. As aresult, the various struts 17 would be heated by unequal amounts. Thisdifference in the heating of the pipes 26 is, however, reduced by theconstruction shown in the drawings since some of the pipes 26 aresupplied with air from the pipes 23 whilst the remaining pipes 26 aresupplied with air from the pipes 24.

The progressive drop in the total pressure head along the pipes 23, 24from the chamber 21 can be reduced if each of the pipes 23, 24 is madeup of a series of portions of progressively reduced internal crosssectional area. Thus the pipes 23 in FIGURE 5 are shown as being formedof portions 30 of successively reduced diameter which fit telescopicallyinto each other and which permit some slight relative axial movement soas to allow for relative expansion therebetween. The arrangement is suchthat the total pressure head in pipes 23 remains substantially constant.In order to compensate for relatively small changes in the totalpressure head along the pipes 23, 24, the bores of the pipes 26 or theircross-sectional areas at the points where they join the pipes 23, 24,may as indicated in FIGURE 6, be progressively increased with distancefrom the chamber 21. If desired the radially inner ends of the pipes 26may be constricted e.g. by providing them with nozzles. This latterarrangement would have the advantage of reducing the effect of the airaccelerating in the pipes 23, 24 into the inlets of the pipes 26, sincemost of the pressure drop of the air passing from the pipes 23, 24 intothe spaces 27 would occur across the constricted ends of the pipes 26.

Each of the pipes 23, 24 (or portions 30 thereof) preferably consists,as shown in FIGURE 6, of coaxial inner and outer skins 31, 32 with anannular layer 33 of a heatinsulating material therebetween. Also, thechamber 21 may have a heat insulating layer around it, or merelycovering the radially inner wall thereof adjacent the air intake 11.

In operation, air which has been heated by being compressed in thecompressor 12 passes via the pipe 22, and chamber 21 to the pipes 23,24. Since the pipes 23, 24 are mounted on the insulating blocks 25, (andsince they are also preferably formed, as indicated in FIGURE 6, with aheat-insulating layer 33) the hot air passing through the pipes 23, 24is not cooled, to any substantial extent, by the cold intake air passingthrough the air intake 11.

The air from the pipes 23, 24 passes via the pipes 26 to the interior ofthe struts 17 so as to prevent the formation of ice on the externalsurface of the latter. Furthermore, all the struts 17 are heated to asubstantially equal extent, whereby the nose cone 16, and the enginebearing carried thereby, will not be displaced due to differentialexpansion of the struts 17.

The hot air which has passed through the annular spaces 27 passes intothe manifold 19 and so to the exhaust port 20. It will be noted fromFIGURE 4 that, since the pipes 24 extend beyond the pipes 23, the spacewithin the exhaust manifold 19 occupied by the inlet manifoldconstituted by the pipes 23, 24 is less adjacent to the exhaust port 20than it is adjacent to the chamber 21. This change in the totalcross-sectional area of the pipes 23, 24 will be more progressive if thepipes 23, 24 have portions of decreasing size as shown in FIGURES 5 and6, in which case the space within the exhaust manifold 19 which is opento the air flow progressively increases towards the exhaust port 2%).Thus the exhaust manifold 19' is formed so that no substantial change oftotal pressure head 'occurs in it towards the exhaust port 243.

In the construction shown in the drawings the hot air which has beenused to heat the struts 17 is passed to atmosphere through the exhaustport 30. If desired, however, this hot air, before being exhausted toatmosphere, can be used to heat the forward part of the nose cone 16 andto heat the leading edge of the air intake 11 as indicated in thepreviously mentioned co-pending application Serial No. 41,347.

With reference to FIGURES 7 and 8, parts corresponding to those of theembodiment shown in FIGURES 1 to 4 have the same reference numerals. Thetop of chamber 21 has an aperture 40 bounded by a peripheral flange 41.The chamber 21 is made rigid by means of four angularly spaced rods 42which extend through and are welded to the top and bottom of the chamber21, the rods 42 also extending through the flange 41. Three furtherbosses 43 are welded to the internal surface of the chamber 21 oppositethe flange 41. An aperture which registers with the aperture 40 is alsoprovided in the top of the manifold 19, and a peripheral flange 45 ofthe inlet pipe 22 abuts the top of the manifold 19 covering the aperturetherein and substantially registering with the flange 41. The pipe 22 issecured to the chamber 21 by seven set screws 46 (only one of which isshown in FIG- URE 7) which engage the screw threaded interiors of thebosses 43 and the rods 42. The pipe 22 therefore communicates with theinterior of the chamber 21, but is sealed from the interior of themanifold 19 by the flange 4'1.

Sole plate 5th is welded to the base 51 of the manifold 19, and thestrut 17 is connected to the sole plate 5t), and the duct 26 isconnected to internal webs 52, 53 and to the wall portions 54, S5 of thesole plate. The cross-sectional view of the sole plate 51 the strut 17and the duct 26 shown in FIGURE 7 has been taken along the median lineof the strut for the sake of simplifying the drawing. The parts 52, 53,54 and 55 of the sole plate 56 blend into an annular ring 58 whichextends through an aperture in the bottom of the chamber 21approximately mid-way between the lateral ends of the chamber 21 wherethe latter has its greatest transverse cross-sectional area as seen inFIGURE 7. This crosssectional area is substantially greater than thetotal crosssectional area of two of the pipes 23, 24 which extend fromone lateral end of the chamber 21. Each of the pi ces 23, 24- is made upof a plurality of arcuate sections A, B, etc., each section joining asucceeding section as indicated in FIGURE 8 after a junction with a duct26.

In FIGURE 9 there is shown the connection of a strut 17 with the pipe 23i.e. at a point spaced from the chamber 21. As shown, the parts 52, 53,54 and 55 extend upwardly to define a U-shaped seating for the pipe 23and an outwardly extending flange 59. An aperture 60 in the sole plate50 registers with an aperture 61 in the tube 23. Straps 62, 63, whichpass round the pipes 23, 24, are bolted to the flange 59 so as to locatethe pipes 23, 24 in position. The side walls of the base of the manifold19 are bolted to the adjoining structures by nuts and bolts indicatedgenerally by the reference numeral 65.

At the radially inner end of the strut 17, the strut extends through anaperture in the nose cone 16 and is connected to an annular hubstructure having front and rear walls 68, 69, dividing walls '70 (seeFIGURE 10), and an inner annulus 71. The radially inner tips of thedividing walls iii are spaced from the annulus 71 so as to permitequalisation of pressure around the hub structure. The hub structure issupported from the nose cone by bolting its rear wall 69 by bolts 74 toan inwardly extending annular flange 75 which is strengthened byangularly spaced webs '76.

It is believed that the operation of this embodiment will be apparentfrom the preceding description, so no detailed account will be given.

The modification described with reference to FIG- URES 7 to 12 differsfrom the arrangement shown in FIGURES 1 to 4 in that there are nineteenof the struts .17, one strut 17 being located directly beneath thechamber 21, and nine struts 17 being arranged on each side of chamber21, each branch of the pipe 23 feeding the first five struts and eachbranch of the pipe 24 feeding the last four struts.

The cross-sectional areas of each of the pipes 23, 24 is approximatelythree to four times greater than the cross-sectional area of the pipe 26as shown in FIG- URE 12, the latter cross-sectional area beingapproximately equal to the total cross-sectional area of the spacebetween the exterior of the pipe 26 and the interior of the strut 17.The total internal cross-sectional area of the manifold 1h i.e.including any space occupied by the pipes 23, 24 is approximately sevento eight times larger than the cross-sectional area of one of the pipes23, 24.

The invention could also be applied to inlet guide vanes of a gasturbine engine in which the angle of each vane is made variable.

I claim:

1. A heat exchange apparatus comprising two spaced apart members, aplurality of struts connecting said members together, a plurality offluid ducts each extending along and being in heat exchange relationshipwith one of said struts, supply manifold means and exhaust manifoldmeans provided on one of said members, both said manifold meanscommunicating with said fluid ducts in succession, supply meansconnected to said supply manifold means for supplying thereto a pressurefluid at a temperature higher than that of said struts, said pressurefluid flowing via said supply manifold means and said fluid ducts intothe exhaust manifold means, the pressure fluid flowing in the supplymanifold means constituting an incoming pressure fluid stream and thepressure fluid flowing in the exhaust manifold means constituting anoutgoing pressure fluid stream, said supply manifold means and saidexhaust manifold means extending together along a common length thereof,and having common wall means along said common length separating saidincoming and outgoing pressure fluid streams, the sum of thecross-sectional area of the supply manifold means through which saidincoming pressure fluid stream flows and the cross-sectional area of theexhaust manifold means through which said outgoing pressure fluid streamflows being substantially constant, said common wall means progressivelydiminishing the crosssectional area of the supply manifold means throughwhich said incoming pressure fluid stream flows, and simultaneouslyprogressively increasing the cross-sectional area of the exhaustmanifold means through which the outgoing pressure fluid stream flowsconsidering the supply and exhaust manifold means in the same directionalong their common length, which direction is the direction of flow ofsaid incoming and outgoing pressure fluid streams whereby the totalpressure heads in said incoming and outgoing pressure fluid streams aremaintained substantially constant.

2. A heat exchange apparatus comprising two spaced apart members, aplurality of struts connecting said members together, a plurality offluid ducts each extending along and being in heat exchange relationshipwith one of said struts, supply manifold means and exhaust manifoldmeans provided on one of said members, both said manifold meanscommunicating with said fluid ducts in succession, supply meansconnected to said supply manifold means for supplying thereto a pressurefluid at a temperature higher than that of said struts, said pressurefluid flowing via said supply manifold means and said fluid ducts intothe exhaust manifold means, the pressure fluid flowing in the supplymanifold means constituting an incoming pressure fluid stream and thepressure fluid flowing in the exhaust manifold means constituting anoutgoing pressure fluid stream, said supply manifold means and saidexhaust manifold means being mounted one within the other with a spacetherebetween over a common length thereof, the inner one of saidmanifold means separating said incoming and outgoing pressure fluidstreams, the cross-sectional area of the outer one of said manifoldmeans being substantially constant, and the inner one of said manifoldmeans having a progressively varying cross-sectional area andprogressively diminishing the cross-sectional area of the supplymanifold means through which said incoming pressure fluid stream flows,and simultaneously progressively increasing the cross-sectional area ofthe exhaust manifold means through which said outgoing pressure fluidstream flows, considering the supply and exhaust manifold means in thesame direction along their common length, which direction is thedirection of flow of said incoming and outgoing pressure fluid streamswhereby the total pressure heads in said incoming and outgoing pressurefluid streams are maintained substantially constant.

3. A heat exchange apparatus as claimed in claim 2 in which said fluidsupply manifold means is disposed within said fluid exhaust manifoldmeans.

4. A heat exchange apparatus as claimed in claim 3 in which said supplymanifold means comprises a plurality of supply pipes each being incommunication with a respective portion of succeeding ones of said fluidducts,

said supply means for supplying pressure fluid to said 4 supply manifoldmeans being common to and communicating with each of said supply pipes.

5. A heat exchange apparatus comprising two spaced apart members, aplurality of struts connecting said spaced apart members together, aplurality of fluid ducts each being in heat exchange relationship withone of said struts, fluid supply manifold means connected to said fluidducts in succession, supply means connected to said fluid supplymanifold means for supplying thereto a pressure fluid at a temperaturehigher than that of said struts, fluid exhaust manifold meanscommunicating with said fluid ducts in succession, said fluid supplymanifold means and said fluid exhaust manifold means being mounted onewithin the other and defining a space therebctween, the fluid flowingfrom the fluid supply manifold means via the fluid ducts to said space,the inner one of said fluid manifold means having a diminishing totalinternal crosssectional area in a downstream direction of fluid flowtherethrough, and said space between said manifold means having anincreasing cross-sectional area in a downstream direction of fluid flowtherethrough whereby total pressure heads in the inner one of said fluidmanifold means and in said space are maintained substantially constant.

6. A heat exchange apparatus as claimed in claim 5 wherein the outer oneof said fluid manifold means has a substantially constant diameterthroughout its length.

7. A heat exchange apparatus as claimed in claim 5 wherein each of saidducts is open ended and is mounted within the respective strut with aspace therebetween, said ducts having fluid flowing therethrough in anopposite direction to direction of flow of fluid in the space betweenthe ducts and their respective struts.

8. A heat exchange apparatus as claimed in claim 7 in which the spacesbetween the struts and the fluid ducts adjacent the open ends of thefluid ducts intercommunicate with one another so as to permit the fluidpressures adjacent said open ends to equalise.

9. A heat exchange apparatus as claimed in claim 5 wherein said spacedapart members are annular and concentric with each other and define anannular air intake therebetween, said struts being disposedsubstantially tangentially of the innermost of said spaced apartmembers, and wherein said fluid supply manifold means and said fluidexhaust manifold means are each arcuate.

References Cited in the file of this patent UNITED STATES PATENTS115,605 Harly June 6, 1871 1,409,259 Sykora Mar. 14, 1922 2,556,736Palmatier June 12, 1951 2,712,727 Morley July 12, 1955

1. A HEAT EXCHANGE APPARATUS COMPRISING TWO SPACED APART MEMBERS, APLURALITY OF STRUTS CONNECTING SAID MEMBERS TOGETHER, A PLURALITY OFFLUID DUCTS EACH EXTENDING ALONG AND BEING IN HEAT EXCHANGE RELATIONSHIPWITH ONE OF SAID STRUTS, SUPPLY MANIFOLD MEANS AND EXHAUST MANIFOLDMEANS PROVIDED ON ONE OF SAID MEMBERS, BOTH SAID MANIFOLD MEANSCOMMUNICATING WITH SAID FLUID DUCTS IN SUCCESSION, SUPPLY MEANSCONNECTED TO SAID SUPPLY MANIFOLD MEANS FOR SUPPLYING THERETO A PRESSUREFLUID AT A TEMPERATURE HIGHER THAN THAT OF SAID STRUTS, SAID PRESSUREFLUID FLOWING VIA SAID SUPPLY MANIFOLD MEANS AND SAID FLUID DUCTS INTOTHE EXHAUST MANIFOLD MEANS, THE PRESSURE FLUID FLOWING IN THE SUPPLYMANIFOLD MEANS CONSTITUTING AN INCOMING PRESSURE FLUID STREAM AND THEPRESSURE FLUID FLOWING IN THE EXHAUST MANIFOLD MEANS CONSTITUTING ANOUTGOING PRESSURE FLUID STREAM, SAID SUPPLY MANIFOLD MEANS AND SAIDEXHAUST MANIFOLD MEANS EXTENDING TOGETHER ALONG A COMMON LENGTH THEREOF,AND HAVING COMMON WALL MEANS ALONG SAID COMMON LENGTH SEPARATING SAIDINCOMING AND OUTGOING PRESSURE FLUID STREAMS, THE SUM OF THECROSS-SECTIONAL AREA OF THE SUPPLY MANIFOLD MEANS THROUGH WHICH SAIDINCOMING PRESSURE FLUID STREAM FLOWS AND THE CROSS-SECTIONAL AREA OF THEEXHAUST MANIFOLD MEANS THROUGH WHICH SAID OUTGOING PRESSURE FLUID STREAMFLOWS BEING SUBSTANTIALLY CONSTANT, SAID COMMON WALL MEANS PROGRESSIVELYDIMINISHING THE CROSSSECTIONAL AREA OF THE SUPPLY MANIFOLD MEANS THROUGHWHICH SAID INCOMING PRESSURE FLUID STREAM FLOWS, AND SIMULTANEOUSLYPROGRESSIVELY INCREASING THE CROSS-SECTIONAL AREA OF THE EXHAUSTMANIFOLD MEANS THROUGH WHICH THE OUTGOING PRESSURE FLUID STREAM FLOWSCONSIDERING THE SUPPLY AND EXHAUST MANIFOLD MEANS IN THE SAME DIRECTIONALONG THEIR COMMON LENGTH, WHICH DIRECTION IS THE DIRECTION OF FLOW OFSAID INCOMING AND OUTGOING PRESSURE FLUID STREAMS WHEREBY THE TOTALPRESSURE HEADS IN SAID INCOMING AND OUTGOING PRESSURE FLUID STREAMS AREMAINTAINED SUBSTANTIALLY CONSTANT.